Base sequence for protein expression and method for producing protein using same

ABSTRACT

To provide a base sequence for protein expression that can increase the yield of protein such as diastatic enzyme by further activating a promoter of a particular gene. A base sequence  1  for protein expression includes: a gene  3  encoding protein  2 ; a promoter  4  of the gene  3 , the promoter being linked upstream of the gene  3 ; and a cis element  5  whose activity is improved by an artificial transcription factor  6 , the cis element being linked further upstream of the promoter  4 . The cis element  5  is represented by SEQ ID NO: 1.

TECHNICAL FIELD

The present invention relates to a base sequence for protein expression for use in the production of protein such as diastatic enzyme using koji mold, and a method for producing protein using the same.

BACKGROUND ART

Heretofore, it has been known that a base sequence for protein expression in which a cis element consisting of a particular base sequence is linked to a promoter of a particular gene that yields protein, when producing protein such as a diastatic enzyme using koji mold (see e.g., Patent Literatures 1 and 2). The conventional base sequence for protein expression can improve the activity of the promoter and can increase the yield of the protein, by linking the cis element to the promoter.

For example, Patent Literature 1 describes a technique of using enhancer DNA consisting of a XlnR/Ace2 binding sequence and a Hap complex binding sequence as a cis element and linking 12 cis elements upstream (on the 5′-terminal side) of a promoter of tef1 gene. According to Patent Literature 1, in this way, GUS activity by the promoter is reported to be improved approximately 4.9 times under solid culture conditions with wheat bran as a carbon source.

Also, Patent Literature 2 describes a technique of using enhancer DNA located at a promoter of α-glucosidasegene of koji mold (Aspergillus oryzae) as a cis element and linking 12 such cis elements upstream (on the 5′-terminal side) of the promoter. According to Patent Literature 2, in this way, GUS activity by the promoter is reported to be improved approximately 6 times under culture conditions with starch as a carbon source.

CITATION LIST Patent Literature [PTL1]

Japanese Patent Application Laid-Open No. 2012-75369

[PTL2]

Japanese Patent No. 3343567

SUMMARY OF INVENTION Technical Problem

However, the conventional base sequence for protein expression merely links a cis element consisting of a particular base sequence to a promoter of a particular gene and is thus desired to be further modified.

In light of these circumstances, an object of the present invention is to provide a base sequence for protein expression that can increase the yield of protein such as diastatic enzyme by further activating a promoter of a particular gene, and a method for producing protein using the same.

Solution to Problem

In order to attain the object, the base sequence for protein expression of the present invention is abase sequence for protein expression comprising: a gene encoding protein; a promoter of the gene, the promoter being linked upstream of the gene; and a cis element whose activity is improved by an artificial transcription factor, the cis element being linked further upstream of the promoter, wherein the cis element is represented by SEQ ID NO: 1, and wherein the artificial transcription factor comprises a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of a transcription factor KojR and an active domain comprising a base sequence of downstream 150 to 604 aa of a transcription factor AmyR, and the active domain is linked downstream of the DNA binding domain, and is represented by SEQ ID NO: 2.

According to the base sequence for protein expression of the present invention, the activity of the cis element represented by SEQ ID NO: 1 linked upstream of the promoter can be improved by the artificial transcription factor represented by SEQ ID NO: 2, and the activity of the promoter can be further improved by the cis element whose activity has been improved. As a result, the activity of the gene is improved by the promoter whose activity has been improved, so that the yield of the protein encoded by the gene can be increased.

The base sequence for protein expression of the present invention preferably comprises a base sequence for artificial transcription factor expression comprising: a gene encoding the artificial transcription factor represented by SEQ ID NO: 2; and a promoter of the gene, the promoter being linked upstream of the gene. According to the base sequence for artificial transcription factor expression, the activity of the gene encoding the artificial transcription factor represented by SEQ ID NO: 2 is improved by the promoter of the gene so that the artificial transcription factor encoded by the gene is produced.

For the base sequence for protein expression of the present invention, it is required that at least one cis element represented by SEQ ID NO: 1 should be linked upstream of the promoter. Preferably, the cis element is linked, for example, at any number in a range of 1 to 10, upstream of the promoter.

The expression vector of the present invention comprises the base sequence for protein expression of the present invention. According to the expression vector of the present invention, a transformant comprising the base sequence for protein expression of the present invention can be produced.

The transformant of the present invention comprises the base sequence for protein expression of the present invention. According to the transformant of the present invention, the yield of the protein encoded by the gene can be increased.

For the transformant of the present invention, it is preferred that koji mold should be used as a host cell, and it is more preferred that the koji mold should be an Aspergillus oryzae HO2strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01750).

The method for producing a protein according to the present invention comprises culturing a transformant comprising the base sequence for protein expression of the present invention, and recovering the protein encoded by the gene expression-enhanced by the base sequence for protein expression, from the medium or the inside of the transformant after the culture.

The base sequence for protein expression of the present invention can increase the yield of the protein encoded by the gene, as mentioned above. Accordingly, when the transformant comprising the base sequence for protein expression of the present invention is cultured, the produced protein accumulates in the medium or the transformant after the culture. Therefore, the protein can be recovered.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative diagram schematically showing the configuration and effect of a base sequence for protein expression of the present invention.

FIG. 2 is an illustrative diagram schematically showing a predicted structure of a transcription factor KojR.

FIG. 3 is an illustrative diagram schematically showing a predicted structure of a transcription factor AmyR.

FIG. 4 is a graph showing a relative value of GUS activity when a transformant of the present invention was cultured for 60 hours with dextrin as a substrate.

FIG. 5 is a graph showing GUS activity when the transformant of the present invention was cultured for 90 hours with dextrin as the substrate.

FIG. 6 is a graph showing GUS activity when the transformant of the present invention was cultured for 60 hours with glucose as a substrate.

DESCRIPTION OF EMBODIMENTS

Next, the embodiments of the present invention will be described further specifically with reference to the attached drawings.

As shown in FIG. 1, a base sequence 1 for protein expression of the present embodiment comprises: a protein gene 3 encoding a desired protein 2; a promoter 4 linked upstream (on the 5′-terminal side) of the protein gene 3; and a cis element 5 linked upstream (on the 5′-terminal side) of the promoter 4.

The protein 2 is, for example, a diastatic enzyme. The protein gene 3 may be any gene which encodes the protein 2.

The cis element 5 is composed of a base sequence comprising enhancer DNA located at a promoter of kojT gene, and the base sequence is gacggaaaagtcgggtagat (SEQ ID NO: 1). In the base sequence 1 for protein expression, 1 to 10, for example, 8 cis elements 5 are linked upstream of the promoter 4.

The base sequence 1 for protein expression also comprises a base sequence 9 for artificial transcription factor expression comprising: an artificial transcription factor gene 7 encoding an artificial transcription factor 6; and a promoter 8 linked upstream (on the 5′-terminal side) of the artificial transcription factor gene 7. The activity of the cis element 5 is improved by the artificial transcription factor 6.

The artificial transcription factor 6 is prepared from a transcription factor KojR 11 shown in FIG. 2 and a transcription factor AmyR 21 shown in FIG. 3. The transcription factors KojR 11 and AmyR 21 are transcription factors both classified into Cys6 cysteine-Zinc cluster type, among transcription factors having a zinc-coordinating DNA binding domain (Zn_Cluster).

As shown in FIG. 2, the transcription factor KojR 11 comprises upstream (5′-terminal side) Zn_Cluster 12 and comprises downstream (3′-terminal side) MHR 13 which is a highly homologous region common in transcription factors classified in Cys6 cysteine-Zinc cluster type. In this context, the transcription factor KojR 11 is composed of a base sequence of 555 aa in full length. The Zn_Cluster 12 is composed of a base sequence of 15 to 45 aa. The MHR 13 is composed of a base sequence of 148 to 281 aa.

In the transcription factor KojR 11, a DNA binding domain associated with binding to the cis element 5 is predicted to reside in a region 14 comprising the upstream Zn_Cluster 12. Examples of a candidate region of the DNA binding domain can include a region composed of a base sequence of 1 to 118 aa, a region composed of a base sequence of 1 to 195 aa, and a region composed of a base sequence of 1 to 239 aa.

On the other hand, as shown in FIG. 3, the transcription factor AmyR 21 comprises upstream (5′-terminal side) Zn_Cluster 22 and comprises a downstream (3′-terminal side) region 23 comprising an active domain. In this context, the transcription factor AmyR 21 is composed of a base sequence of 604 aa in full length. The Zn_Cluster 22 is composed of a base sequence of 13 to 52 aa.

Examples of a candidate region of the active domain in the transcription factor AmyR 21 can include a region composed of a base sequence of 113 to 604 aa, a region composed of a base sequence of 150 to 604 aa, a region composed of base sequence of 219 to 604 aa, and a region composed of a base sequence of 257 to 604 aa.

Accordingly, the artificial transcription factor of the present embodiment has a configuration (SEQ ID NO: 2) in which an active domain comprising a base sequence of downstream 150 to 604 aa of the transcription factor AmyR is linked downstream of a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of the transcription factor KojR.

According to the base sequence 1 for protein expression of the present embodiment, as shown in FIG. 1, the artificial transcription factor 6 encoded by the artificial transcription factor gene 7 whose activity has been improved by the promoter 8 in the base sequence 9 for artificial transcription factor expression is produced, and the produced artificial transcription factor 6 binds to the cis element 5. The activity of the cis element 5 is improved by the binding to the artificial transcription factor 6. The activity of the promoter 4 is improved by the cis element 5 whose activity has been improved.

Then, the activity of the protein gene 3 is improved by the promoter 4 whose activity has been improved, so that the protein 2 encoded by the protein gene 3 whose activity has been improved, is produced. As a result, the base sequence 1 for protein expression of the present embodiment can increase the yield of the protein 2.

Next, Examples of the present invention will be shown.

Example 1

(Construction of Transformant Introduced with Artificial Transcription Factor Gene)

In this Example, first, the genomic DNA gene of an Aspergillus oryzae HO2strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01750) was used as a template in PCR to amplify an upstream sequence of tppA gene using primers 1 and 2, its downstream sequence using primers 3 and 4, a tef1 promoter gene using primers 5 and 6, anagdA terminator gene using primers 7 and 8, and a gene fragment for marker recycling using primers 9 and 10, while the genomic DNA gene of an Aspergillus awamori HA strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01751) was used as a template in PCR to amplify a gene cassette for pyrG gene expression using primers 11 and 12. DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD FX neo) was used in each PCR amplification. The amplification products were each purified using a purification kit (manufactured by Qiagen N.V., product name: QIAquick PCR purification kit) to obtain a total of 6 gene fragments.

Next, an E. coli-derived plasmid pMD20 (manufactured by Takara Bio Inc.) was used as a template in PCR to amplify a gene fragment derived from the plasmid using primers 13 and 14 and the DNA polymerase. The amplification product was purified using the purification kit to obtain the gene fragment.

Next, these 7 gene fragments were sequentially treated with a cloning kit (manufactured by Takara Bio Inc., product name: In-Fusion HD Cloning kit) and used in the transformation of an E. coli HST08strain (manufactured by Takara Bio Inc.) to construct a plasmid pPT.

Next, the plasmid pPT was treated with a restriction enzyme SmaI (manufactured by Takara Bio Inc.) at 30° C. and purified using the purification kit to obtain the restriction treatment product of the plasmid (gene fragment).

Next, the genomic DNA gene of an Aspergillus oryzae HO02 strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01750) was used as a template in PCR to amplify a DNA binding domain of a transcription factor KojR using primers 15 and 16 and an active domain of a transcription factor AmyR using primers 17 and 18. The DNA polymerase was used in each PCR amplification. The amplification products were each purified using the purification kit to obtain the DNA binding domain and the active domain.

Next, the DNA binding domain and the active domain were treated with the cloning kit and used in the transformation of an E. coli HST08 strain to construct a plasmid carrying an artificial transcription factor gene in which the DNA binding domain and the active domain were joined together.

The plasmid carrying the artificial transcription factor gene was used as a template in PCR to amplify a gene fragment for koji mold transformation using primers 19 and 20 using DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD-plus-neo). The amplification product was purified using the purification kit to obtain the gene fragment for koji mold transformation.

Next, an Aspergillus oryzae HO2 strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01750) was transformed with the gene fragment for koji mold transformation according to the standard method of the PEG-calcium technique. Subsequently, the obtained transformants were screened for a strain capable of growing in a CD plate medium to obtain a transcription factor-producing strain.

Next, the transcription factor-producing strain was inoculated at 1×10⁶ cells/plate to a CD medium supplemented with fluoroorotic acid monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (final concentration: 1 mg/mL) and uridine (manufactured by Sigma-Aldrich Inc.) (final concentration: 20 mM) and screened for a strain capable of growing therein to obtain a uridine-auxotrophic transcription factor-producing strain.

The base sequences of the primers 1 to 20 are shown in Table 1.

TABLE 1 SEQ Primer ID No. Base sequence 5′→3′ NO Remarks  1 ccggctcgtatgttgctggaccaaccgccaaggttag  3 Upstream sequence of tppA gene  2 actgaattgcaattaatggcggacaatg  4 Upstream sequence of tppA gene  3 tgtctcggaccttacgtgtcttagatgcgactcaatacaactgttc  5 Downstream sequence of tppA gene  4 tgggtaacgccagggttgaggctgaagacttaaatacgacattgc  6 Downstream sequence of   tppA gene  5 Ctgttacgcttccccgggtttgaaggtggtgcgaactttgtagttc  7 tef1 promoter gene  6 gtaaggtccgagacagtaagggattgatc  8 tef1 promoter gene  7 taattgcaattcagtagtaacccattcccggttctctagctg  9 agdA terminator gene  8 gtaacgccagggcccggggaagcgtaacaggatagcctagacccac 10 agdA terminator gene  9 ctgcaggatgattagcgtgcaaaccaagcaaacaagcatc 11 Gene fragment for marker recycling 10 actgaattgcaattaatggcggacaatg 12 Gene fragment for marker recycling 11 taattgcaattcagtgcaagctcgagcatccaactaaactag 13 Gene cassette for pyrG gene expression 12 tgggtaacgccagggcccgggctaatcatcctgcagctccgtcattg 14 Gene cassette for pyrG gene expression 13 ccctggcgttacccaacttaatcg 15 Plasmid-derived gene fragment 14 caacatacgagccggaagcataaagtg 16 Plasmid-derived gene fragment 15 cgcaccaccttcaaaatgtcgttgaataccgacgattccggtc 17 DBD of transcription factor kojR 16 gcctgagtacaaggagcccaatgc 18 DBD of transcription factor kojR 17 atcctgttacgcttctcaaaacgaaatctcctccccagcc 19 AD of transcription factor AmyR 18 tccttgtactcaggcgcactccccgcgccac 20 AD of transcription factor AmyR 19 cagtgagcgcaacgcaattaatgtgagttag 21 Gene fragment for koji mold transformation 20 gggatgtgctgcaaggcgattaagttg 22 Gene fragment for kojimold transformation [Construction of GUS-Producing Strain with Cis Elements Linked]

First, a first gene fragment in which: 4 cis elements of SEQ ID NO: 1 were linked in tandem; restriction enzyme sites SphI and BamHI were added on the 5′-terminal side thereof; and BglI and NcoI sites were added on the 3′-terminal side thereof was prepared by oligo synthesis.

Next, the first gene fragment and a plasmid pPEA2 containing an Aspergillus oryzae-derived enoA promoter were each fragmented by treatment with restriction enzymes SphI and NcoI. These fragments were subjected to ligation reaction, and E. coli was then transformed with the ligation product to construct a plasmid pEA4K.

Next, the gene fragment was treated with a restriction enzyme BamHI, while the plasmid pEA4K was treated with restriction enzymes BglII and NcoI. These two treatment products were subjected to ligation reaction, and E. coli was then transformed with the ligation product to construct a plasmid pEA8K.

Next, the plasmid pEA8K was used as a template in PCR amplification using primers 21 and 22 and DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD-plus-). The amplification product was purified using a purification kit (manufactured by Promega Corp., product name: Wizard SV Gel and PCR Clean-Up System) to obtain a second gene fragment.

Next, the genomic DNA of Aspergillus oryzae was used as a template in PCR amplification using primers 23 and 24 and DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD-plus-). The amplification product was purified using a purification kit (manufactured by Promega Corp., product name: Wizard SV Gel and PCR Clean-Up System) to obtain a third gene fragment.

Next, the second gene fragment and the third gene fragment were used as a template in fusion PCR using primers 22 and 24 to prepare a fourth gene fragment in which the second gene fragment and the third gene fragment were joined together.

Next, a restriction enzyme-treated plasmid pPPG introduced with an E. coli-derived plasmid pMD20 (manufactured by Takara Bio Inc.) carrying upstream 1000 bp of Aspergillus oryzae-derived pyrG gene, an Aspergillus oryzae-derived pyrG expression cassette, and an E. coli-derived uidA gene was subjected to ligation reaction with a gene fragment for marker recycling obtained by PCR-amplifying a plasmid pPPG as a template using primers 25 and 26 and DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD-plus-) and purifying the amplification product using a purification kit (manufactured by Promega Corp., product name: Wizard SV Gel and PCR Clean-Up System). Then, E. coli was transformed with the ligation product to construct a plasmid pPPRG.

Next, the plasmid pPPRG was used as a template in PCR amplification using primers 27 and 28 and DNA polymerase (manufactured by Toyobo Co., Ltd., product name: KOD-plus-). The amplification product was purified using a purification kit (manufactured by Promega Corp., product name: Wizard SV Gel and PCR Clean-Up System) to obtain a fifth gene fragment.

The fourth gene fragment and the fifth gene fragment were used as a template in fusion PCR using primers 24 and 27 to prepare a cis element-linked GUS (β-glucuronidase) production cassette gene fragment in which the fourth gene fragment and the fifth gene fragment were joined together.

Next, the uridine-auxotrophic transcription factor-producing strain was transformed using the cis element-linked GUS production cassette gene fragment according to the standard method of the PEG-calcium technique. Subsequently, the obtained transformants were screened for a strain capable of growing in a CD plate medium to obtain a GUS-producing strain with 8 cis elements linked in tandem.

The base sequences of the primers 21 to 28 are shown in Table 2.

TABLE 2 Primer SEQ No. Base sequence 5′→3′ ID NO 21 ccgctgctaggcgcgccgtgcactatagggcgaattgggc 23 22 tggggtttctacaggacgtaacattttgacgagctgcggaattg 24 23 cacggcgcgcctagcagcgggtagtggtggatacgtactcctt 25 24 ttcaggtcacgttctaagcttatcag 26 25 cccccctccggatgatgtagaagttgctcggtagctg 27 26 cccccctccggacaattgccgcgaaaaattaaattg 28 27 ccagaggtgactttatccaagatt 29 28 caattccgcagctcgtcaaaatgttacgtcctgtagaaacccca 30

[GUS Activity Measurement Method]

The GUS-producing strain with 8 cis elements linked in tandem was cultured in a CD plate medium for 1 week to form spores. The spores were recovered using 0.01% POLYSORBATE 20 (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain a spore suspension.

Next, 50 mL of a PD medium (2 mass/volume % of dextrin, 1 mass/volume % of polypeptone, 0.1 mass/volume % of casamino acid, 0.5 mass/volume % of potassium dihydrogen phosphate, 0.05 mass/volume % of magnesium sulfate, and 0.1 mass/volume % of sodium nitrate) was placed in a 200 mL Erlenmeyer flask, to which the spores were then inoculated at a final spore concentration of 1×10⁵/mL.

Next, liquid culture was performed at 30° C. for 60 hours. After the completion of the culture, the bacterial cells were disrupted, and the disrupted powder was suspended in a buffer for intracellular protein extraction having the composition given below to obtain an extract.

[Composition of Buffer for Intracellular Protein Extraction]

NaH₂PO₄•2H₂O (MW = 156.01) (pH 7) 1.56 g (50 mM) 0.5M EDTA   4 mL (10 mM) Nonionic surfactant (manufactured by Sigma-Aldrich  0.2 g (0.1%) Inc., product name: Triton X-100) N-Laurylsarcosinate Na  0.2 g (0.1%) β-mercaptoethanol (MW = 78.13)  142 μL (10 mM) Distilled water  200 mL

Next, the extract was added to a buffer for GUS activity measurement having the composition given below and reacted at 37° C. for 15 minutes. Then, the absorbance was measured at a wavelength of 415 nm to calculate an activity value (U). 1 U means the amount of the enzyme necessary for forming 1 mM PNP from PNP-Glucuronide (purine nucleoside phosphorylase-glucuronic acid inclusion) at 37° C. for 1 minute.

[Composition of Buffer for GUS Activity Measurement]

NaH₂PO₄•2H₂O (MW = 156.01) (pH 7) 1.56 g (50 mM) β-mercaptoethanol (MW = 78.13)  142 μL (10 mM) Nonionic surfactant (manufactured by Sigma-Aldrich  0.2 g (0.1%) Inc., product name: Triton X-100) p-Nitrophenyl β-D-glucuronic acid inclusion   63 mg (1 mM) (MW = 315.23) Distilled water  200 mL

Next, the amount of the protein contained in the extract was measured using protein assay CBB solution (manufactured by NacalaiTesque, Inc.), and the activity value was divided by the amount of the protein to calculate GUS activity (U/mg). The results are shown as a relative value of GUS activity in FIG. 4.

Also, GUS activity (U/mg) when the liquid culture was performed at 30° C. for 90 hours is shown in FIG. 5.

Comparative Example 1

In this Comparative Example, a GUS-producing strain was constructed in totally the same way as in Example 1 except that the artificial transcription factor gene was not introduced and no cis element was linked.

Next, GUS activity was measured in totally the same way as in Example 1 except that the GUS-producing strain obtained in this Comparative Example was used.

A relative value of GUS activity (U/mg) when the liquid culture was performed at 30° C. for 60 hours is shown in FIG. 4. GUS activity (U/mg) when the liquid culture was performed at 30° C. for 90 hours is shown in FIG. 5.

From FIG. 4, when the GUS activity (U/mg) in which the liquid culture was performed at 30° C. for 60 hours with dextrin as a substrate is defined as 1 for the GUS-producing strain of Comparative Example 1 in which the artificial transcription factor gene was not introduced and no cis element was linked, it is obvious that 8.2 times GUS activity can be obtained in the GUS-producing strain of Example 1.

From FIG. 5, when the GUS activity (U/mg) when the liquid culture was performed at 30° C. for 90 hours with dextrin as a substrate is defined as 1 for the GUS-producing strain of Comparative Example 1 in which the artificial transcription factor gene was not introduced and no cis element was linked, it is obvious that 8 times GUS activity can be obtained in the GUS-producing strain of Example 1.

Example 2

In this Example, GUS activity (U/mg) was calculated in totally the same way as in Example 1 except that 50 mL of a PG medium (2 mass/volume % of glucose, 1 mass/volume % of polypeptone, 0.1 mass/volume % of casamino acid, 0.5 mass/volume % of potassium dihydrogen phosphate, 0.05 mass/volume % of magnesium sulfate, and 0.1 mass/volume % of sodium nitrate) was placed in a 200 mL Erlenmeyer flask, to which the spores of the GUS-producing strain harboring 8 cis elements linked in tandem obtained in Example 1 were then inoculated at a final spore concentration of 1×10⁵/mL, followed by liquid culture at 30° C. for 60 hours. The results are shown in FIG. 6.

Comparative Example 2

In this Comparative Example, GUS activity was measured in totally the same way as in Example 2 except that the GUS-producing strain obtained in Comparative Example 1 was used. GUS activity (U/mg) when the liquid culture was performed at 30° C. for 60 hours is shown in FIG. 6.

From FIG. 6, when the GUS activity (U/mg) in which the liquid culture was performed at 30° C. for 60 hours with glucose as a substrate is defined as 1 for the GUS-producing strain of Comparative Example 2 in which the artificial transcription factor gene was not introduced and no cis element was linked, it is obvious that 4.6 times GUS activity can be obtained in the GUS-producing strain of Example 2.

REFERENCE SIGNS LIST

-   1 base sequence for protein expression -   2 protein -   3 gene -   4 promoter -   5 cis element, and -   6 artificial transcription factor 

1. A base sequence for protein expression comprising: a gene encoding protein; a promoter of the gene, the promoter being linked upstream of the gene; and a cis element whose activity is improved by an artificial transcription factor, the cis element being linked further upstream of the promoter, wherein the cis element is represented by SEQ ID NO: 1, and wherein the artificial transcription factor comprises a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of a transcription factor KojR and an active domain comprising a base sequence of downstream 150 to 604 aa of a transcription factor AmyR, and the active domain is linked downstream of the DNA binding domain, and is represented by SEQ ID NO:
 2. 2. The base sequence for protein expression according to claim 1, comprising a base sequence for artificial transcription factor expression comprising: a gene encoding the artificial transcription factor; and a promoter of the gene, the promoter being linked upstream of the gene.
 3. The base sequence for protein expression according to claim 1, wherein in the base sequence for protein expression the cis element is linked at any number in a range of 1 to 10 upstream of the promoter of the gene encoding the protein.
 4. An expression vector including a base sequence for protein expression, the base sequence for protein expression comprising: a gene encoding protein; a promoter of the gene, the promoter being linked upstream of the gene; and a cis element whose activity is improved by an artificial transcription factor, the cis element being linked further upstream of the promoter, wherein the cis element is represented by SEQ ID NO: 1, and wherein the artificial transcription factor comprises a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of a transcription factor KojR and an active domain comprising a base sequence of downstream 150 to 604 aa of a transcription factor AmyR, and the active domain is linked downstream of the DNA binding domain, and is represented by SEQ ID NO:
 2. 5. The expression vector according to claim 4, wherein the base sequence for protein expression comprises a base sequence for artificial transcription factor expression comprising: a gene encoding the artificial transcription factor; and a promoter of the gene, the promoter being linked upstream of the gene.
 6. The expression vector according to claim 4, wherein in the base sequence for protein expression, the cis element is linked at any number in a range of 1 to 10 upstream of the promoter of the gene encoding the protein.
 7. A transformant including a base sequence for protein expression, the base sequence for protein expression comprising: a gene encoding protein; a promoter of the gene, the promoter being linked upstream of the gene; and a cis element whose activity is improved by an artificial transcription factor, the cis element being linked further upstream of the promoter, wherein the cis element is represented by SEQ ID NO: 1, and wherein the artificial transcription factor comprises a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of a transcription factor KojR and an active domain comprising a base sequence of downstream 150 to 604 aa of a transcription factor AmyR, and the active domain is linked downstream of the DNA binding domain, and is represented by SEQ ID NO:
 2. 8. The transformant according to claim 7, wherein the base sequence for protein expression comprises a base sequence for artificial transcription factor expression comprising: a gene encoding the artificial transcription factor; and a promoter of the gene, the promoter being linked upstream of the gene.
 9. The transformant according to claim 7, wherein in the base sequence for protein expression, the cis element is linked at any number in a range of 1 to 10 upstream of the promoter of the gene encoding the protein.
 10. The transformant according to claim 7, wherein koji mold is used as a host cell.
 11. The transformant according to claim 10, wherein the koji mold is an Aspergillus oryzae HO2strain (National Institute of Technology and Evaluation, Patent Microorganisms Depositary, #122, 2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan, Deposition Date: Nov. 12, 2013, Deposition No.: NITE BP-01750).
 12. A method for producing protein, comprising culturing a transformant including a base sequence for protein expression which comprises: a gene encoding the protein; a promoter of the gene, the promoter being linked upstream of the gene; and a cis element whose activity is improved by an artificial transcription factor, the cis element being linked further upstream of the promoter, wherein the cis element is represented by SEQ ID NO: 1 and recovering the protein encoded by the gene expression-enhanced by the base sequence for protein expression, from a medium or inside of the transformant after the culture, wherein the artificial transcription factor comprises a DNA binding domain comprising a base sequence of upstream 1 to 195 aa of a transcription factor KojR and an active domain comprising a base sequence of downstream 150 to 604 aa of a transcription factor AmyR, and the active domain is linked downstream of the DNA binding domain, and is represented by SEQ ID NO:
 2. 13. The method for producing protein according to claim 12, wherein the base sequence for protein expression comprises a base sequence for artificial transcription factor expression comprising: a gene encoding the artificial transcription factor; and a promoter of the gene, the promoter being linked upstream of the gene.
 14. The method for producing protein according to claim 12, wherein in the base sequence for protein expression, the cis element is linked at any number in a range of 1 to 10 upstream of the promoter of the gene encoding the protein.
 15. The method for producing protein according to claim 12, wherein the transformant is cultured by using a medium including kojic acid. 